Abstract:
The speed governor problems in a high hydro-ratio power grid will lead to ultra-low frequency oscillations with the frequency below 0.1 Hz, which is mixed with the low frequency oscillation increasing difficulty to identify low frequency oscillation parameters. Therefore, an adaptive time-frequency analysis method-nonlinear mode decomposition(NMD) to identify the parameters of low frequency oscillations is proposed. The method can extract the time-frequency ridge according to the signal structure, obtained the harmonic parameters; identifying true harmonics of the corresponding components, the false mode components are eliminated. And it uses the spectral entropy characteristics of the extracted components to set a stop decomposition criterion, making the decomposed nonlinear mode(NM) components have practical physical significance. The oscillation parameters of each NM component are identified with Hilbert transform(HT). Finally, the method is analyzed and validated by self-synthesized signal simulation, the four-machine two-zone system simulation and the real data collected from the power grid. The effectiveness and feasibility of the proposed method are verified by the results.